The present invention concerns in general terms a method and device for determining the quantity of product present in a reservoir, and more particularly for determining the quantity of ink present in the reservoir of an image formation device. The present invention also concerns a product reservoir, notably an ink reservoir for an image formation device. It also concerns a device for processing electrical signals intended to be used in a device for determining the quantity of product present in a reservoir.
For image formation devices, such as printers, which use ink jet technology, numerous devices and methods have been designed for determining the quantity of ink present in the reservoir.
The document U.S. Pat. No. 4,700,754 describes a device for detecting the quantity of liquid ink in a flexible reservoir contracting as the ink level decreases. The external bottom wall is coated with a conductive layer constituting one pole of a capacitor. The wall of the reservoir serves as a dielectric of the capacitor thus produced whilst the ink surface in contact with the bottom wall constitutes the second pole of the capacitor. A measuring electrode placed at the centre of the reservoir connects the ink to a measuring device. When the ink level decreases, the surface area of ink facing the conductive layer coated on the wall decreases, and therefore the value of the equivalent capacitance also decreases. The fact that the reservoir is flexible enables the measuring electrode to remain in contact with the ink.
This type of detection is used for a cartridge having flexible walls and cannot be applied to rigid cartridges. This is because contact between the measuring circuit and the ink can be made only if the top wall, when it is crushed, forces the measuring electrode to be in contact with the ink.
In addition, it is necessary to provide an electrode in contact with the ink in the reservoir, which complicates the manufacture of the reservoir and increases the cost thereof.
Moreover, it is difficult to know the ink level if the latter is below a level lying between the measuring electrode and the bottom wall. This is because the measuring electrode cannot go down as far as the base of the reservoir. The measurement range is thus limited in the lower values. However, it is precisely when there is very little ink remaining in the reservoir that it is advantageous to be alerted so as to change the reservoir or fill it.
The document EP-A-0 028 399 describes a device for detecting a minimum quantity of ink in a reservoir. A resonant circuit includes a resistor and a capacitor whose poles are formed by two metal plates between which the ink reservoir is situated. The reservoir containing the ink forms the dielectric of the capacitor. As the quantity of ink decreases, the value of the capacitance of the capacitor thus formed varies.
The resonant circuit is calibrated so that its resonant frequency corresponds to a predetermined quantity of ink in the reservoir. The maximum voltage at the terminals of the resistor is thus achieved for this predetermined quantity of ink which constitutes a threshold.
By measuring the voltage at the terminals of the resistor of the resonant circuit, the passing of the threshold is detected, and a warning signal is activated.
According to this document, only the passing of a threshold is measurable, and consequently only a quantity of ink can be detected. Under these circumstances, this device is of interest if the quantity of ink detected is small, in order to alert the user just before the end of the reservoir.
However, it is very difficult with this device to determine accurately what voltage corresponds exactly to a small quantity of ink. It is then necessary to provide a safety margin in order to alert the user before the reservoir is empty. This safety margin, for example around 20 per cent of the total quantity of ink, results in a waste of ink, since the user will change the reservoir whilst there is still ink inside.
The present invention aims to remedy the drawbacks of the prior art by providing a device and method for determining the quantity of product present in a reservoir, which detects, with satisfactory reliability and with precision, a predetermined quantity of product, whilst being simple and economical to implement.
The invention starts from the idea according to which generating an electrical field in the reservoir produces a signal representing the quantity of product in the reservoir. However, the inventors have found that this signal can be used only in a limited range of quantities.
This is because, with certain types of alternating electrical fields characterised by a frequency of around 0.5 to 2 MHz, the representation of the quantity of product as a function of the signal is biunivocal within a product quantity range; the signal can therefore be used directly in this range in order to determine the quantity of product. However, the representation of the quantity of product as a function of the signal is not biunivocal outside this range; outside this range, there is therefore uncertainty about the quantity of product.
The inventors then discovered that, by increasing the frequency, the representation was biunivocal for all the quantity values (from 0 to 100%). However, for certain types of reservoir the inventors once again found a scatter in the electrical characteristics of the reservoirs from one example to another, thereby giving rise to uncertainty about the quantity outside a range in which the signal is usable.
In this context, the invention proposes a method for determining the quantity of product present in a reservoir, characterised in that it includes the steps of:
establishing, through the product present in the reservoir, a first electrical field, and a second electrical field which is differentiated from the first electrical field by at least one characteristic,
measuring the said first and second electrical fields passing through the product, in order to produce first and second electrical signals respectively representing the first and second electrical fields, and
processing the first electrical signal in order to produce a first information signal able to take a plurality of values representing the quantity of product then present in the reservoir,
taking into account, in order to determine the quantity of product, at least one range of quantities in which this representation is directly usable, and
processing the second electrical signal in order to produce, at the appropriate time, a second information signal representing at least one predetermined quantity outside the said range.
The present invention resolves the above-mentioned problems and makes it possible to obtain a usable measurement of the quantity of product in a reservoir over all the quantity values (from 0 to 100%).
In particular, providing a second electrical field differentiated by at least one characteristic from the first, advantageously removes the uncertainties mentioned above outside the range in which the first information signal is directly usable, whether these uncertainties are due to the fact that the representation is not biunivocal outside this range, or whether they are due to the scatter in electrical behaviour observed from one reservoir to another.
In general terms, the invention applies to any product, notably a consumable product used in a given device.
The invention preferably applies to ink contained in the reservoir of an image formation device. xe2x80x9cInkxe2x80x9d here means any liquid, solid, gaseous or powder product designed to modify an optical or physical factor of the printing medium.
The present invention also has the advantage of being adaptable to a large number of existing devices.
The invention applies to cases where several interchangeable reservoirs can be used in succession. This occurs for example for image formation devices in which ink reservoirs of different colours can be used successively. The user fits the reservoir of the desired colour at a given moment and makes as many changes of reservoir as necessary.
In fact, the measurement performed by virtue of the invention requires no storage in memory of successive measurements, and only the measurements performed instantaneously are useful for determining the quantity of product present in the reservoir and for detecting the predetermined quantity of product present in the reservoir.
In a preferred embodiment, the product is connected to a predetermined potential and the second electrical signal is processed in order to produce, at the appropriate time, an information signal corresponding to the interruption of the connection of the product to the predetermined potential, the said interruption itself corresponding to a predetermined quantity outside the said range.
This characteristic is particularly advantageous since the second signal is processed in order to detect only the interruption of the connection of the product to a potential, which is not only easy to implement but is also particularly reliable because of the simplicity of the criterion used.
According to another characteristic which is simple to implement in this embodiment, the step of processing the second electrical signal includes the comparison of the second electrical signal with a second threshold in order to detect the interruption of the connection of the product to the predetermined potential.
According to another characteristic of the invention which is also easy to implement, the step of processing the first electrical signal includes the detection of the amplitude of the first electrical signal and the production of the signal representing the quantity of product from a value given by a calibration table as a function of the amplitude detected.
According to yet another preferred characteristic of the invention, the method includes the comparison of the first electrical signal with a first threshold in order to determine whether the quantity of product present in the reservoir is situated in the said range, or whether the second electrical field must be established through the product present in the reservoir.
This comparison makes it possible to distinguish whether the quantity of product present in the reservoir is close to the predetermined quantity, and it is then only in such case that the second electrical field is applied in order to find out whether the predetermined quantity has been reached. Thus it is not necessary to apply the second electrical field to the product if, according to the first electrical signal, the quantity of product present in the reservoir is not close to the predetermined quantity.
Advantageously, the method also includes the step of displaying a representation of the quantity of product present in the reservoir and of the predetermined quantity of product present in the reservoir, or the step of transmitting the signal representing the quantity of product present in the reservoir, or the predetermined quantity of product present in the reservoir, to a remote device so that it will display a representation of the quantity of product present in the reservoir.
This product being a consumable product used in a given device, the user knows at any time the quantity of product remaining in the reservoir.
The user is alerted to the fact that the predetermined quantity has been reached. For example, if this quantity is zero or almost zero, he can fill the reservoir or replace it with a full reservoir.
According to another aspect, the invention concerns a device for determining a quantity of product present in a reservoir, characterised in general terms in that it has:
means of establishing first and second electrical fields through the product present in the reservoir, the second field being differentiated from the first by at least one characteristic,
means of measuring the first and second electrical fields in order to produce first and second electrical signals respectively representing the said first and second electrical fields, and
means of processing the first electrical signal so as:
to produce a first information signal able to take a plurality of values representing the quantity of product then present in the reservoir,
to take into account, in order to determine the quantity of product, at least one range of quantities in which this representation is directly usable,
to produce, at the appropriate time, from the first electrical signal, a second information signal representing at least one predetermined quantity outside the said range.
The device according to the invention is particularly well suited to implementing the method briefly disclosed above. This device also has analogous advantageous.
In a preferred embodiment, the device also has means of connecting the product to a predetermined potential, whilst the processing means are adapted to produce, at the appropriate time, from the second electrical signal, an information signal corresponding to the interruption of the connection of the product to the predetermined potential, this interruption itself corresponding to a predetermined quantity outside the said range.
This device has advantages similar to those of the preferred implementation of the method according to the invention set out above.
According to a preferred characteristic of the invention, the establishment means include first and second metallic elements disposed outside the reservoir. The first and second metallic elements form the poles of a capacitor, whose dielectric is formed by the reservoir containing the product.
According to preferred characteristics, the establishment means are fed by oscillators selectively connected to the establishment means via a selector, and the first and second electrical fields are produced by alternating signals, for example with frequencies substantially equal to 1 MHz and 10 khz respectively.
The inventors have determined that these frequencies optimise the determination of the quantity of product and the determination of the predetermined quantity of product.
The difference in characteristics between the electrical fields is due to the difference in frequency of the signals used to produce the electrical fields.
According to a preferred embodiment which is simple and economical to implement, the measuring means include an envelope detector and an analogue to digital converter for producing a digital signal representing the amplitude of the first or second electrical signal.
According to preferred characteristics, the device also includes a means of displaying a representation of the quantity of product present in the reservoir.
It also includes a means of displaying a representation of the predetermined quantity of product present in the reservoir.
The user is thus effectively informed about the quantity of product present in the reservoir.
In another aspect, the invention proposes a product reservoir, characterised in that it has connection means designed to connect the product to a predetermined potential, with a view to detecting the interruption of the connection of the product to the predetermined potential, the said interruption corresponding to at least a predetermined quantity of product present in the reservoir.
In the case of an image formation device, the connection means are advantageously included in the ink ejection means. The connection means are thus common with the ink ejection means, and the connection of the product to the predetermined potential then requires no additional element to be included in the reservoir, nor consequently any additional manufacturing step, which is particularly economical.
The reservoir according to the invention is particularly suited to equipping the above device and makes it possible to obtain advantages analogous to those disclosed above.
The invention also concerns a cartridge including this ink reservoir.
The present invention also concerns a processing device including the means of processing the first and second electrical signals means as briefly defined above.